It could be, yes. The universities and colleges will want to discuss your application and qualifications with you, not with your parents, advisers or friends. Vacancies can be filled extremely quickly so if you're not around at the start of Clearing, places on your chosen course may have gone to other people. Better to confirm your place before having a break!
Even if you have been accepted, you may still need to be available. All universities and colleges have different procedures for applying for/confirming accommodation, registering etc so it is best to check with the one you will be attending to see when you would need to be available before you book a holiday. If you do need to be away, it is helpful to nominate someone else who can act on your behalf. We'll need their details, so please contact our Customer Contact Centre.